Very high requirements are imposed upon valves especially insofar as they are used to control the flow of gaseous mediums in medical applications. On the one hand, it is intended that the resistance to flow should be as small as possible for the opened condition and, on the other hand, it is considered important that a complete seal be provided in the closed condition. Furthermore, the effort required to actuate the valve should be of a low level. The movable masses should be held as small as possible in order to maintain the impact forces associated with the movement of the valve and the generated sound as low as possible.
Especially with respect to the last-mentioned condition, valve types have been introduced wherein two essentially plate-shaped valve components are disposed opposite each other at a relatively short spacing. These valve components can be designated as a valve plate and as a valve member. The valve plates have openings which are covered over by the valve member in the closed condition of the valve. The sealing lines are therefore essentially formed by the peripheral lines of the openings.
A short-stroke drive is provided for actuating the valve and moves the valve element and the valve plate relative to one another. The valve plate is usually fixedly mounted and the short-stroke drive moves the valve member in a direction perpendicular to the surface of the plate. The stroke length of the short-stroke drive is only a fraction of the diameter of the plate.
A valve of this kind is described, for example, in German published patent application DE-OS No. 30 06 298. In this valve, the stationary valve plate has two ring lands which conjointly define an annular channel therebetween in which the medium to be controlled can enter via a corresponding ring-shaped line. The valve member has two ring lands lying opposite corresponding ones of the ring lands of the valve plate so that the ring lands of the valve member and of the valve plate press against each other in the closed condition and define sealing lines. The valve member is driven by a piezo-electric drive.
Low actuating power and a low-noise movement are achieved in the known valves by means of the short stroke length. The flow resistance is relatively low notwithstanding the short stroke length because of the relatively large cross-sectional surface of the valve plate and the openings contained therein. However, a considerable effort is required in order to obtain an adequate seal when viewed in the context of the long sealing lines which are required. For this reason, plate valves of this kind have not gained acceptance especially for valves of small configuration.